you need to create a hash algorithm. and you need a database.once a player registers - you send him a game key (example: 3D5B8-A3B8-etc.. ) and for that key you save yourself a HASH that is generated once you pull through the whole key. (example, you get something like this: a7asdas7a6d876asdgdk12jb124).

that algorithm must give the same hash for that cd key EVERY TIME. so when someone uses that CD KEY if hash is correct - enable download to that person (or whatever). OF course you can't control if it's the same person, but kinda does half of the anti-piracy job (example: i buy your game and give cd key to some friend. he plays your game like he's me but he's not me )

Sea Monsters template - Isometric Also includes 40 pages PDF of optimizations and "how-to" for your games, and how the "sea monsters" template was built. Follow link for details :)